I think all I'd consider either way with regards to an eating disorder is that they can look different on everyone.
Not everyone who has an eating disorder starves themselves or is massively underweight. It can be bingeing but not always purging, avoiding certain food groups, even just a preoccupation with food.
I won't claim to be an expert, trained in or have experience with but I did used to work in education there was lots of warning signs we had to look out for.
I don't want to assume either way with Grace and I'm sure to some people she has a really healthy attitude to food, just like to some others she has an unhealthy attitude. It's so subjective. But she is very slim, gives the impression of eating a lot and is starting to get to the age where metabolism slows.